Changes in Level of Several Functional Components and ACE-Inhibitory Activity in Developing Soybean Seeds

Soybean quality is determined based on protein content, lipid content and fatty acid composition, and several functional components including isoflavones, anthocyanins and functional activity. Because the level of each component changes during seed development, it is necessary to know the concentration of quality-related components in developing seeds. Little is known of the pattern of changes in quality-related components. Seeds from field-grown soybean was harvest from the $R_6$ stage to the $R_8$ stage in 2004. Seed characteristics and the level of nutritional components were examined. Seed moisture content was dropped rapidly after the $R_7$ stage in the tested varieties. Seed growth rate was the highest from the beginning of the $R_6$ stage to the mid-$R_6$ stage. Chlorophyll content was decreased rapidly in pods and seeds. However, seed growth period from the $R_6\;to\;R_8$ was 35 days. The crude protein content was. increased dramatically between 63 DAF and 70 DAF and then increased slightly. The pattern of isoflavone accumulation was nearly similar to that of seed weight increase. From the late $R_6$ stage to the $R_7$, the accumulation rate was higher as compared to other stages. The angiotensin inhibitory activity was increased according to seed development from 63 ($R_6$) to 84 DAF ($R_8$). The difference of inhibitory activity in heated soybean powder, however, was not great among stages. The inhibitory activity was affected by heating treatment. The most effective heating time was 10 min. Excessive heating longer than 30 min resulted in a lowered inhibitory activity of soybean on ACE.